1. Field of the Invention
This invention relates to a light deflecting apparatus for deflecting the angle of emergence of an incident light beam.
2. Description of the Prior Art
It is known to cause information light modulated by information signals to be deflected by the use of a mirror or other deflecting means and cause the modulated light to scan over a scanned surface on which a photosensitive medium is disposed, thereby effecting recording of the information signals or read-out of the information on the scanned surface. There have been devised various types of such light deflecting apparatus, one of which is the rotatable polygon mirror type light deflecting apparatus. This rotatable polygon mirror type light deflecting apparatus is high in deflection speed and capable of continuous light deflection and therefore, capable of recording or reading out high-density information at high speed.
FIG. 1 of the accompanying drawings is a cross-sectional view of a scanning optical system using a conventional rotatable polygon mirror type light deflecting apparatus.
In FIG. 1, reference numeral 1 designates a rotatable polygon mirror, 2 the outer case of the light deflecting apparatus, 3 an incidence window glass, 4 an image forming f.multidot..theta. lens, 9 a beam expander, 10 a light modulator, and 11 an He-Ne laser. The incidence window glass 3 is attached to the outer case 2 by a window glass keeper 5 secured to the outer case 2 by means of a screw 6, and the f.multidot..theta. lens 4 is mounted by being screwed into a lens adapter 7 secured to the outer case 2 by means of screws 8. The outer case 2 shields the rotatable polygon mirror 1 from the ambient air to prevent the mirror surface of the rotatable polygon mirror 1 from being contaminated by dust, oil or the like in the air.
The laser beam B emitted from the He-Ne laser 11 is modulated by the light modulator 10 in accordance with recording information or the like and has its beam diameter expanded by the beam expander 9 and passes through the incidence window glass 3 to the rotatable polygon mirror 1. Further, the laser beam B is deflected by the mirror surface 1a whose angle is being varied by the rotation of the rotatable polygon mirror 1, and forms an image on a scanned surface (not shown) with the aid of the f.multidot..theta. lens 4.
Heretofore, when recording or read-out of information is effected by the use of a light deflecting apparatus, it has been common practice to use He-Ne or like gas laser as the light source, as shown in FIG. 1, but the gas laser is bulky in size and has suffered from a disadvantage that it occupies extensive space in the system. In contrast, a semiconductor laser which has made its advent in recent years is much smaller in size than the gas laser and has the function of a light modulator as well and, if a semiconductor laser could be used in such a scanning optical system, it would be possible to make the scanning optical system compact.